Very high speed commercial digital presses print variable data at rates of thousands of pages per minute. Typically, the receiver that is printed is in the form of a web that is transported past stationary printheads. During transport, the web has considerable inertia and cannot be readily subjected to rapid changes in speed. It is desirable to continuously transport the web at a constant speed or with relatively slow speed adjustments.
The continuous transport of receiver also necessitates a continuous supply of data in the form of printable frames. This data must be buffered so as to be available as needed. Considerable time is required to fill a buffer with the printable frames, since the print job is initially supplied in a different form and is converted. That conversion is typically in the form of raster image processing and is performed by one or more downstream processors. The processing speed that defines the sustained output speed of each of the downstream processors is generally limited by the content of the input data, since the time to raster image process a frame tends to be highly data dependant. It is possible to define frames that take a substantial amount of time to prepare for output. Another limitation that affects the raster image processing is the supply of input data to the downstream processors. Variable data supplied by a secondary source can be subject to limitations of communication bandwidth or the processing capability of a host computer. With many print jobs, different portions of the job are simultaneously buffered, being raster image processed, and not yet delivered to the raster image processor.
It would thus be desirable to provide improved systems and methods.